The hole for the blank is made about 1⁄64 inch larger in diameter than the designated size of the bolt, to permit of the easy extraction of the blank after it is upset, this extraction being accomplished by striking the end of the tongue with the hammer. If the block is made of cast iron the upper end of the hole will become worn after forging five hundred or six hundred bolts, leaving the bolts with a rounded neck, as at c c in [Fig. 2906]; a steel block, however, will forge several thousand bolts without becoming enlarged.
Fig. 2907.
An excellent plan is to provide the block with removable dies, such as at d d in [Fig. 2907], which are easily renewed, a number of such dies having different diameters of bore fitted to the same block.
When the bolt end is sufficiently reset or enlarged to form the head it is laid in a bottom swage, containing three of the six sides of the hexagon, and a hammer blow on the uppermost part of the end forges a flat side. After each blow the work is revolved one-sixth of a revolution, and as the angles of the swage are true they obviously true the angles of the bolt head. After the head has been roughed down it is necessary to flatten it again under the head and on the end, for which purpose it may be placed in the heading block shown in [Fig. 2904], after which the sides of the head may be finished and the cupping tool for chamfering the head applied.
The bolt may require passing from the heading tool to the swage several times, as forging it in one direction spreads it in another.
Fig. 2908.